I don't think it's over powered, just hard to stop from a site-lock perspective.
DD doesn't really help. If I'm playing a disciples deck against sites, I'm not going to put more than one or two disciples into Fishing Boat at a time (and I generally avoid putting more than 3 into it at a time). So DD is going to take out one disciple...that leaves at least 8 more, or 10 if you're playing with the Red guys. Plus, I can always get him back with Resurrection or CoF.
You only have to wait a turn when you first draw it. As long as you have several disciples out, after first turn setup, you can put one under and add a new one to the boat every turn until you run out of disciples (and Philip can pull Bartholomew back into play from under the deck). A site-lock deck is going to be more focused on locking people out than winning battles, so if they can't get rid of my access, there's not much they can do if I have a few disciples and something like MLaMG in hand and/or Lay Down Your Life out.
